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 *** The Mega Super Awesome Visuals Company ***
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#pragma once

#include "ofMain.h"
#include "ofxMSAConstraint.h"

class ofxMSASpring : public ofxMSAConstraint {
public:
	friend class ofxMSAPhysics;

	float restLength;
	float strength;

	ofxMSASpring(ofxMSAParticle *a, ofxMSAParticle *b, float _strength, float _restLength) {
		this->_a = a;
		this->_b = b;
		strength	= _strength;
		restLength	= _restLength;
		_type = OFX_MSA_CONSTRAINT_TYPE_SPRING;
		setClassName(string("ofxMSASpring"));
	}


protected:
	void solve() {
		ofPoint delta = (*_b) - (*_a);
		float deltaLength2 = msaLengthSquared(delta);
		float deltaLength = sqrt(deltaLength2);	// TODO: fast approximation of square root (1st order Taylor-expansion at a neighborhood of the rest length r (one Newton-Raphson iteration with initial guess r))
		float force = strength * (deltaLength - restLength) / (deltaLength * (_a->getInvMass() + _b->getInvMass()));

		if (!_a->isFixed()) *_a += delta * (_a->getInvMass() * force);
		if (!_b->isFixed()) *_b -= delta * (_b->getInvMass() * force);
 	}


    void debugDraw() {
        ofSetColor(0, 255, 0);
        ofxMSAConstraint::debugDraw();
	}

};
